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Sys, Shutil, and OS Modules

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Sys, Shutil, and OS Modules This video will introduce the sys, shutil, glob, and os modules. 1 The sys module contains a few tools that are often useful and will be used in this course. The first tool is the argv function which allows the script to request a parameter when the script is run. We will use this function in a few weeks when importing scripts into ArcGIS. If a zero is specified for the argv function, then it will return the location of the script on the computer. This can be helpful if the script needs to look for a supplemental file, such as a template, that is located in the same folder as the script. The exit function stops the script when it reach the exit statement. The function can be used to stop a script when a certain condition occurs – such as when a user specifies an invalid parameter. This allows the script to stop gracefully rather than crashing. The exit function is also useful when troubleshooting a script. 2 The shutil module contains tools for moving and deleting files. The copy tool makes a copy of a file in a new location. The copytree tool makes a copy of an entire folder in a new location. The rmtree tool deletes an entire folder. Note that this tool will not send items to the recycling bin and it will not ask for confirmation. The tool will fail if it encounters any file locks in the folder. 3 The os module contains operating system functions – many of which are often useful in a script. The makedirs tool will create a new folder including any intermediate folders. The listdir tool will list the basenames of the files located in a folder. The rmdir tool will delete an empty folder. The remove tool will delete a file And the rename tool will change the name and location of the original file to the new name and location that is specified. 4 Let’s consider a few applications of the tools that we’ve discussed so far. In this example, we’ll have the script create a temporary workspace where it will store intermediate files. At the end of the script, the entire temp workspace will be deleted. This code defines a temp workspace location and creates it using the os.makedirs tool. Arcpy’s default workspace is set to the temp workspace. At the end of the script, the shutil.rmtree tool is used to delete the temp workspace. 5 In this example, the script will process a set of files contained in the same workspace. The os.listdir tool gets a list of the files located in the workspace. 6 Now that we have a list of file names, we can process those files using a for loop. In the loop, we need to join the file basename to its workspace so that the script can find the file. The os.path.join tool is convenient for building a full file pathname from a workspace and basename. The loop can then process the file as needed 7 The glob module will get a list of files in a workspace. It is similar to the os.listdir tool except that glob allows the use of a wild card. The asterisk is a wild card character that can be used in place of any part of the file name – the glob tool returns any file names that satisfy the portion of the file name that was specified. 8 The os.path module contains tools for working with file path names. Note that here I’ve explicitly imported all tools in the os.path module so you will not see the module name appear in the statements below. The exists tool returns a true or false value depending on whether the script is able to find the specified file or workspace. The basename tool will return the basename of a file path name. The dirname tool will return the workspace in a file path name. The getsize tool will return the file size in bytes. The join tool will join a workspace and a basename to create file path name. 9 The splitext tool will return a list in which the file extension is separated from the file pathname. The split tool will return a list containing both the file workspace and the basename. There are also tools that will get the times that the file was last accessed, last modified, and created. These times are in seconds since a reference time called an epoch. We’ll learn how to convert these times to a more meaningful format when we discuss the time module in the next video. 10 The os module’s chdir command allows you to change Python’s default workspace (a.k.a working directory). This is equivalent to setting the arcpy workspace – however, Python’s default workspace only applies to Python tools. Recall that arcpy’s workspace setting only applies to arcpy tools. 11 Let’s look at an example of working with the os.path module. In this example, the workspace and basename were parsed (i.e. extracted) from a file in order to provide the required input parameters for the CreateFeatureclass ArcTool. The dirname tool was used to extract the workspace and the basename tool was used to extract the basename of the file. Note that the same task could have been accomplished using the os.path’s split tool – there are often a number of ways to accomplish a given task in a script. Having the script parse information from a file name can help reduce the number of parameters that a user must specify when running the script. 12.
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